Thursday, September 10, 2009

H1N1 Flu May Have Peaked

As students were returning to college campuses, there was the biggest concentration of flu cases so far, at least since the H1N1 flu virus became widespread earlier this year. There was a surprising rush of suspected cases reported in the last week of August and first few days of September. Since then, it looks like the number of cases has fallen off by almost half.

I’m drawing this conclusion after looking at the pace of personal flu reports on Twitter and comments from officials on specific university campuses that describe the rush of flu cases as something in the recent past.

A USA Today story theorizes that sorority and fraternity rush events were the scene for many of the new flu infections. That could account for the sudden spike in flu cases. More than 10 percent of students on some campuses contracted flu in August.

It is too early to say, but it is likely enough that that was the peak of H1N1 in the United States. The rapid decline in cases this week shows that the flu is not following the exponential growth pattern that is expected in the classic model of a highly infectious pandemic. Either the H1N1 virus is not as infectious as expected or it does not spread quite the same way flu viruses did in years past, perhaps because of precautions such as washing hands and hand-contact surfaces and keeping infected individuals away from public spaces when possible.

The timing is ironic, because health workers are still “gearing up” for a flu season that may have peaked already. Typically, the winter flu season in North America does not get going until November.